Representation of Complex Dynamic Spectra in Auditory Cortex
Abstract
Recent neurophysiological experiments have shed new light onto how various sound features are encoded and organized in the primary auditory cortex (AI). One such feature is the envelope of broadband acoustic spectra, or spectral profile, the most important physical correlate of timbre (Plomp 1976). To determine how AI units represent complex dynamic profiles, it is essential to measure their spectro-temporal response field (STRF). This function is analogous to the receptive field of visual neurons in that it reflects the strength and dynamics of the unit responses to tones at different frequencies. A more traditional response measure of auditory units is the response area , defined roughly as the range of tone frequencies and intensities that just elicit excitatory or inhibitory responses. The response area is only useful as a qualitative predictor of a unit's responses to arbitrary broadband spectra; its measurements is also significantly affected by a host of experimental difficulties and nonlinear factors that render estimates of parameters such as bandwidth and asymmetry quantitatively inaccurate (Shamma 1993, Shamma et al. 1995a, Nelken et al. 1994). To circumvent some of these problems, we have used new techniques to measure the spectral and dynamic properties of response areas in AI (Schreiner and Calhoun 1995, Shamma et al. 1995a). The stimuli and techniques adapted from vision research (De Valois 1990) and from psychoacoustic studies (Green 1986, Hillier 1991, Summers and Leek 1994) apply linear system theory to measure the response area of cortical units. Specifically, they employ broadband spectra with sinusoidally modulated profiles against the logarithmic frequency axis or ripples shown in Fig.1. By varying the ripple density (or frequency), amplitude, and drift velocity, one can measure a transfer function to such rippled spectra, and from it by an inverse Fourier transform obtain the STRF.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1997
- Accession Number
- ADA483813
Entities
People
- Didier A. Depireux
- Jonathan Z. Simon
- Shihab A. Shamma
Organizations
- University of Maryland